But while the presidential candidates have blown off all but a handful of swing states, a group of true-blue and deep-red states have become battlegrounds in another campaign: the fight for control of the House of Representatives.

The two parties also have targeted 18 other House races in states without a close presidential contest. Democrats are hoping to gain four GOP seats in Minnesota, while Republicans dream of capturing Democratic seats in Connecticut, Rhode Island and Massachusetts.

“Orphan states are playing an outsized role in the House landscape this year,” said Zach Hunter, a spokesman for the Congressional Leadership Fund, a group working to elect Republicans. “States like California and New York will be central in the battleground for the House for the next decade.”

Because most states seem certain to back either Obama or Romney, these “orphan states” give both parties an unusual opportunity to broadcast messages to voters uncluttered by the presidential nastiness.

“When you don't have to think about the presidential race because it's not being thrust upon you (in television commercials), then the voter can think of things closer to home and come to a not-predetermined decision,” said Ed Costantini, a political scientist at the University of California at Davis.

The “orphan state” effect is magnified by the availability of TV ad time. In many presidential swing states, television stations are sold out of advertising space through the election, so groups trying to influence congressional elections are likely to focus on other states.

“There's going to be a lot of attention (on those states) in the days ahead,” said Gary Rose, chairman of the government and politics department at Sacred Heart University in Connecticut.

Among the high-profile contests:

• Texas' 23rd District, where freshman Republican Francisco “Quico” Canseco and Democratic state Rep. Pete Gallego are locked in a close race in a majority-Latino district that is evenly divided along partisan lines.

• New York's 19th District race, where redistricting forced Albany-area Republican Chris Gibson to seek a second term in a more Democratic district with a large bloc of new voters.

• California's 52nd District, where six-term San Diego Republican Brian Bilbray is trying to hold off Democrat Scott Peters, a former city council president, in a newly designed district that is almost evenly divided among Republicans, Democrats and Independents.

• Minnesota's 8th District, where Republican Chip Cravaack ousted powerful Democratic committee chairman Jim Oberstar two years ago but now faces a stiff challenge from former Duluth City Councilor Jeff Anderson in a Democratic-leaning district.

• New York's 21st District race, where Democrat Bill Owens has won two elections with less than 50 percent of the vote but now faces a united GOP in a district with a 15 percentage-point Republican registration edge.

• Connecticut's 5th District, where Republicans are hoping to take back a swing seat currently represented by Democrat Chris Murphy, who is running for the U.S. Senate this year.

Democrats say Romney's presidential campaign missteps have put Republican incumbents on the defensive all over the country, but most significantly in heavily Democratic states such as California, New York and Illinois.

“The Romney-Ryan ticket is an anchor around House Republican candidates in these ‘orphan states,' and it's getting heavier by the day,” said Jesse Ferguson, spokesman for the Democratic Congressional Campaign Committee. Democrats say they still expect to win many of the 71 House districts carried by President Barack Obama but represented in Congress by a Republican. To maximize their opportunities, DCCC executive director Robby Mook says the party has built “a sophisticated turnout operation” in California, Illinois and New York.

Republicans respond that redistricting has given them the potential to pick up seats in many of these same Democratic states, including up to four in California and two in New York and Illinois.

What's more, the GOP expects to gain half a dozen Democratic seats in heavily Republican states such as Utah, Georgia, Arkansas and Oklahoma.